Manufacturing of Micromirrors used in Projection Systems

BADI SAI NIHANTH REDDYDEPARTMENT OF MECHANICAL

ENGINEERING

Nanosystems Principles Poster Session – Fall 2015

INTRODUCTION• Micromirror devices are devices based on microscopically small mirrors and

commonly known as Digital Micromirror Device (DMD).

• Micromirror arrays are spatial light modulators that can modulate incident light’s phase or amplitude

• DMD chip consists of pressure sensors, accelerometers and micro actuators

DMD chip Micromirror array DMD pixels

PROJECTION SYSTEMS

FILM PROJECTORS

• A film is fed on to the projector.

• A source light projects the image from the film onto the screen.

•System has many mechanical components and the system is very complicated.

• The film degrades over time producing scratches and dirt.

DIGITAL PROJECTORS

• This system is a combination of mechanical, optical and electronic components.

• It consists of a micromirror array that can modulate incident light’s phase or amplitude.

• Simple system with less components.

Film Projectors Digital Projectors

PRINCIPLE• Each micromirror in the array is considered as a pixel having bi-stable

operation of ±12o.

• When the mirror is tilted +12o the light is passed through the projector lens and when it is tilted -12o, the light is tilted away from the projected lens on to the light absorber.

Bi-stable operation of DMD pixel Torsion State of micromirror

FABRICATION1) Fabrication using membrane transfer bonding

• Thick silicon nitride is deposited and an aluminum layer is sputtered.

• The electrodes and the probing pads are patterned and wet etched.

• A sacrificial layer is bonded to the target using low temperature adhesive wafer bonding.

• By DRIE and grinding the sacrificial layer is removed to free the silicon micromirror.

Fabrication of micromirror by wafer transfer bonding

• Deposition of silicon nitride and patterning of photoresist with KOH mask.

• Etching to obtain the V grooves, back nitride with RIE and silicon using DRIE.

• Pattern photoresist on the wafer backside and etch Au and Cr on backside.

• Etch oxide on wafer backside to open windows for DRIE.

• DRIE etch through wafer to form the micromirror structures.

2) DRIE Fabrication

Schematic illustration of the micromirror array fabrication process.

APPLICATIONSOptical Scanners • Galvanometric and Resonant optical

scanners.• Galvanometric type produces a steady-state

deflection and follows a control waveform with considerable fidelity.

• Resonant type operates, only at, or near the resonance of the system, where the system oscillates harmonically.

Micromirror-based Zoom Lens

• Lens have different focal length and work same as an optical zoom lens, also known as smart lens.

• Lenses are arranged in a polar grid array, i.e. in concentric circles

Schematic layout of an integrated scanning-display module

Control of tilt angle of the mirror

High-quality, real-time holographic displays

• Holography is based on light diffraction and interference.

• Present technology has limited scaling limits around 2-4 mm, by which the projection angle is limited to 10 degrees.

• A high resolution display must have up to 8 million pixels, which is very insufficient for visualization of a 3D scene.

• HoloDis system has 1 million submicron diffractive devices on a single chip with a diffracting angle of 30o and a 15 o projection angle HoloDis System

Holography

SCOPE OF MICROMIRRORS

• Decorating 2D gold microplates with magnetic nanoparticles for high contrast between on and off state.

• Optical colloid can be actuated with magnetic field.

Laser Headlights

• Laser head lights provides a glare-free high beam.

• The light is projected in the form of a user defined image, only in the places without light, rejecting the light from, by modulating the power of the laser beam.

 Bulk magnetic microplate solution under an applied magnetic field

with various orientations (θ) relative to the viewing direction

Laser headlights